1. Field of the Invention
The present invention relates to a stacked type dielectric filter in which a resonance electrode is formed in a dielectric substrate constructed by laminating a plurality of dielectric layers.
2. Description of the Related Art
Recently, as the wireless communication system such as portable telephones is diversified, the demand is increased for the realization of a stacked type dielectric filter having a small size and a filter for the wireless system having a low frequency. In view of such a trend, in the conventional stacked type dielectric filter, the Q value of the resonator is improved and the electrostatic capacity between the resonance electrodes is increased by superimposing the plurality of resonance electrodes in the stacking direction so that a high performance filter having a small size is realized.
A conventional stacked type dielectric filter 100 is shown in FIG. 11A. The stacked type dielectric filter 100 comprises two sets of resonators (first and second resonators 104A, 104B) which are arranged in a dielectric substrate 102. Each of the resonators 104A, 104B comprises, for example, three sheets of resonance electrodes 106A to 106C which are superimposed in the stacking direction. A dielectric layer is allowed to intervene between the resonance electrodes 106A and 106B in the stacking direction. A dielectric layer is allowed to intervene between the resonance electrodes 106B and 106C in the stacking direction.
However, in the case of the conventional stacked type dielectric filter 100, the resonance electrodes 106A to 106C having an identical width are superimposed in the stacking direction. Therefore, the following problem arises. That is, for example, as shown in FIG. 11B, the spacing distance C between the resonators 104A, 104B is changed due to stacking deviations arising during production, and the inductive coupling between the resonators 104A, 104B is changed. When the spacing distance C between the resonators 104A, 104B is shortened, the inductive coupling between the resonators 104A, 104B is strengthened.
FIG. 11B is illustrative of a case in which the resonance electrode 106B at the second layer is deviated in the rightward direction. In this case, the spacing distance C between the resonators 104A, 104B is the distance between one long side (long side opposed to the second resonator 104B) of the second resonance electrode 106B of the first resonator 104A and one long side (long side opposed to the first resonator 104A) of the first or third resonance electrode 106A or 106C of the second resonator 104B. It is understood that the spacing distance is shortened by an amount of the stacking deviation as compared with the normal spacing distance C shown in FIG. 11A.
For example, in the case of a stacked type dielectric filter of the capacitive coupling type in which the attenuation pole is in a low band as compared with a pass band, when the inductive coupling is strengthened, the pass band width of the filter is narrowed. In the case of a stacked type dielectric filter of the inductive coupling type in which the attenuation pole is in a high band as compared with a pass band, when the inductive coupling is strengthened, the pass band width of the filter is widened.
As described above, the conventional stacked type dielectric filter involves such a problem that it is difficult to obtain desired characteristics due to the stacking deviation during the production.
The present invention has been made taking the foregoing problems into consideration, an object of which is to provide a stacked type dielectric filter which makes it possible to decrease the variation of characteristics even when stacking deviations occur in a plurality of resonance electrodes during production and which makes it possible to maximally exhibit the effect (high Q value, small size, and high performance) to be obtained by constructing a resonator by superimposing the plurality of resonance electrodes in the stacking direction.
According to the present invention, there is provided a stacked type dielectric filter comprising at least two sets of resonators arranged in a dielectric substrate constructed by laminating a plurality of dielectric layers, in which the resonator includes a plurality of resonance electrodes superimposed in a stacking direction; wherein at least one resonance electrode of the plurality of resonance electrodes for constructing the resonator is formed to have a wide width as compared with the other resonance electrode.
Accordingly, even when stacking deviations occur when the plurality of resonance electrodes are stacked, the other electrode is included in the wide-width resonance electrode as viewed in plan view. Therefore, the spacing distance between the resonators is dominated by the spacing distance between the wide-width resonance electrodes of the respective resonators. Even when stacking deviations occur in the other resonance electrode, then the spacing distance between the resonators is scarcely changed, and the inductive coupling is scarcely changed as well.
As described above, in the stacked type dielectric filter according to the present invention, even when stacking deviations occur in the plurality of resonance electrodes during production, it is possible to decrease the variation of characteristics. It possible to maximally exhibit the effect (high Q value, small size, and high performance) to be obtained by constructing the resonator by superimposing the plurality of resonance electrodes in the stacking direction.
In the stacked type dielectric filter constructed as described above, it is preferable that a stacking deviation amount, which is brought about when the plurality of resonance electrodes for constructing the resonator are stacked so that respective central positions are coincident with each other, is smaller than a protruding amount of the resonance electrode having the wide width with respect to the other resonance electrode.
It is preferable that when a number of the resonance electrodes for constructing the resonator is an odd number; a resonance electrode, which is located at a center in the stacking direction, is the resonance electrode having the widest width.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.